1. Field of the Invention
The present invention relates to an optical ferrule having a plurality of optical fiber insertion holes and guide pin holes, and a manufacturing method thereof.
2. Description of the Related Art
As a conventional optical ferrule, there is an optical ferrule used for an optical connector (JIS C 5981: corresponding to an F12 type multicore optical fiber connector) which is generally called an MT connector and which uses a fitting pin positioning method. This optical ferrule has an approximately rectangular structure including optical fiber insertion holes arranged in a row and guide pin holes for positioning on both sides thereof. Generally, from the viewpoint of productivity and costs, the MT connector is integrally molded by transfer molding or injection molding using resin.
If an optical ferrule has a structure integrally molded, the productivity of the optical ferrule is improved. However, there is a problem that such optical ferrule has a complicated mold structure. Moreover, there is also a problem that it is difficult to manufacture a high-precision product with high yield.
Japanese Patent Application Laid-Open Publication No. 2002-156553 (Japanese Patent No. 3574620, Patent Document 1) discloses an optical ferrule manufactured by taking into consideration the problems described above. According to Patent Document 1, as shown in FIGS. 1 and 2, an optical ferrule 3 has a positioning block 1 and a ferrule main body 2. The positioning block 1 is previously resin-molded so as to allow highly accurate formation of a plurality of optical fiber insertion holes 1a and guide pin holes 1b on both sides thereof. The ferrule main body 2 is formed by molding a resin over the positioning block 1. On upper and lower surfaces of the positioning block 1, protrusions 1c are formed. In the ferrule main body 2, formed are: a hollow part 4 including an optical fiber introduction opening 4a and an adhesive filling window 4b; and guide grooves 5 facing the optical fiber insertion holes 1a. 
As described above, the optical ferrule 3 is formed by molding the resign over the positioning block 1. Therefore, when accuracy of an arrangement pitch or holes for the optical fiber insertion holes 1a and the guide pin holes 1b in the positioning block 1 is improved, not very high accuracy is required for the ferrule main body 2. Moreover, since the resin molding for the ferrule main body 2 is easy, there is an advantage that an inexpensive optical ferrule can be manufactured.
For a general optical ferrule that is integrally molded so as to include optical fiber insertion holes, high-precision molding is difficult. One of the reasons for this difficulty is that the resin in the ferrule is unevenly distributed to cause distortion of the ferrule during shrinkage on curing of the resin.
A mold structure for preventing deterioration in the accuracy is expensive and requires a complicated manufacturing process. Therefore, there arises a problem that yield for molding is significantly lowered and that manufacturing costs are significantly increased.
Regarding the above problem, in Patent Document 1, a block is prepared for positioning optical fibers, for which high accuracy is required. Thereafter, a frame body is formed around the block by overmolding. Specifically, a portion including the optical fiber insertion holes, for which high accuracy is required, and other portions are separately manufactured. The accuracy is more easily improved in the optical ferrule disclosed in the above document than in the general integrally molded optical ferrule. Furthermore, management of the manufacturing process and also the mold structure are simplified. Thus, the yield is improved and the optical ferrule can be manufactured at low cost.
The arrangement of the optical fiber insertion holes is not limited to one-dimensional arrangement including only one row of optical fiber insertion holes (one optical fiber insertion hole array) as shown in FIG. 2, and may be two-dimensional arrangement having a plurality of optical fiber insertion hole arrays.